This invention relates to a process and apparatus for treating wastewater.
Declining water tables, population growth, increasing industrialization, expanding use of irrigated agriculture, and pollution of fresh water supplies strain limited fresh water supplies around the world. Reclaimed wastewater can serve as a supplemental source of water, particularly for non-potable uses. Irrigation of crops and landscaping, which constitutes approximately 70% of total water demand and which also benefits from some of the nutrients present in wastewater, represents one suitable non-potable use for reclaimed water. Other appropriate non-potable applications for reclaimed wastewater include washing, cooling, fire prevention and control, creek enhancement, recreational ponds, cement preparation, dust control, and toilet flushing. Despite the wide range of non-potable uses, wastewater reclamation typically has been practiced only on a very small scale. Conveyance of reclaimed water from the reclamation site to a site of use and limited production methods can represent obstacles to more widespread use of reclaimed water.
Effective and efficient treatment of wastewater is economically and environmentally important. Wastewater treatment systems can include incineration systems, chemical treatment systems, electrolysis systems, nuclear radiation systems, and physical treatment systems. These various systems can provide water of varying quality. Many of theses systems can be costly and relatively difficult to run and maintain. Physical treatment systems such as filtration can be difficult to develop because of fouling problems and retarded flow. In addition to chemical and pathogenic impurities, incoming wastewater can include settleable solids, such as hard and abrasive materials, that can damage components of the treatment system and floatable materials, such as fats, oils, greases and fibers that can foul a physical treatment system. Useful systems for wastewater treatment can provide consistent output, be capable of automation, be relatively small in size, provide usable liquid and solid byproducts, and be relatively low in cost.
In general, the invention features a process and apparatus for treating wastewater streams into beneficial water and solids components using membrane separation as a principal treatment. Removal and segregation of materials that adversely affect operation of the membrane separator earlier in the treatment process can improve water throughput, water quality and the lifespan of system components. Physical separation of settleable solids and floatable materials from the wastewater prior to treatment with a membrane separator can allow higher flow rates to be achieved.
In one aspect, the invention features a method for treating wastewater containing settleable solids to form a reusable liquid fraction. The method includes separating a wastewater stream into a first component and a second component in a first containment zone, applying the second component to a membrane permeable to selected ingredients of the second component, and concentrating the second component on a surface of the membrane to form a solids concentrate and a reusable liquid fraction. The first component includes an amount of settleable solids greater than an amount of settleable solids in the second component. The method can include comminuting the wastewater stream prior to separating the first component and the second component. High shear forces can be created between the second component and the membrane.
In certain embodiments, separating can also include settling settleable solids by forces generated by wastewater stream flow into a separation tank, by gravity, or by combinations thereof.
The reusable liquid fraction can be disinfected. This can be accomplished by, for example, exposing the reusable liquid fraction to ultraviolet radiation. In certain embodiments, disinfecting can include mixing a chemical oxidant, such as ozone, with the reusable liquid fraction.
The reusable liquid fraction can be applied to unsaturated soil. The soil can assist in removal and productive reuse of plant nutrients contained in the reusable liquid fraction, and return purified water to underlying aquifers.
The method can include removing the solids concentrate from the membrane as a slurry fraction and returning the slurry fraction to the wastewater stream. The method can include passing the reusable liquid fraction through a filter system either prior to or following membrane separation. The filter system can be backflushed, for example, to create a volume of backflushed material and that can be combined with the slurry fraction. The filter system can include a fixed-film biofilter. Contact with the film of the biofilter can result in removal of remaining suspended solids, nitrification of dissolved and suspended nitrogen compounds, and reduction of other sources of biochemical oxygen demand. The biofilter can be backflushable.
The wastewater can be obtained from a sewer. The first component and the froth fraction can be combined to form a slurry stream that can be returned to the sewer downstream of the location from which the wastewater was obtained. In certain embodiments, the slurry stream can be passed into a third containment zone to separate it into a supernatant fraction and a settled fraction. Sufficient retention time in the third containment zone can allow for substantial settling of settleable solids to the bottom of the zone. In the third containment zone, solids can be decomposed by a predominantly anoxic biological process. The supernatant fraction can be returned to the first containment zone or the second containment zone, or passed to an underground leach field.
In another aspect, the invention features an apparatus for treating wastewater containing settleable solids. The apparatus includes a settleable solids separator, which includes a vessel having an upper end, a lower end, and an outer wall connecting the upper end and the lower end. The settleable solids separator also includes an inlet directed partially tangentially through the outer wall of the vessel, a first outlet proximate to the upper end of the vessel, and a second outlet proximate to the lower end of the vessel. The apparatus also includes a membrane separation system having an inlet and a permeate outlet. The inlet and the permeate outlet are separated by a membrane. A fluid conduit fluidly connects the first outlet of the settleable solids separator and the inlet of the membrane separation system. The membrane separation system can also include a concentrate port. Motive pressure applied to the membrane separation system inlet can be provided by a feed pump in fluid communication with the inlet.
The settleable solids separator can be a vortex separator. The settleable solids separator can also include a vent and overflow port positioned between the first outlet and the upper end of the vessel. The second outlet of the settleable solids separator can be a settled solids outlet in communication with an opening in the base of the vessel for removing solids, which are swept towards the opening by a vortex.
In certain embodiments, an equalization vessel, that can have an upper end, a lower end, and an outer wall connecting the upper and lower end, can be included between the first outlet of the settleable solids separator and the inlet of the membrane separation system. The vessel can also include a scum overflow and vent port between the normal liquid level of the vessel and the upper end. The inlet of the equalization vessel can be below the first outlet of the separator. The outlet port of the equalization vessel can be at the lower end.
The membrane separator system feed pump can receive as input clarified wastewater provided either directly from the first outlet of the settleable solids separator, or in certain embodiments, from the outlet port of an equalization vessel. The apparatus can also include a filter system, which has an inlet and a filtrate outlet, with the inlet in fluid communication with the feed pump, and the filtrate outlet in fluid communication with the membrane separation system feed inlet. The filter system can be a backflushable filter system, a fixed-film biofilter system, or a backflushable fixed-film biofilter system. The backflushable filter can include filter disks.
A permeate conduit can fluidly connect the permeate outlet of the membrane separation system with a disinfection system, which can include an ultraviolet disinfection system or an ozone treatment system, or both. The ozone treatment system can include a closed ozone treatment vessel having an ozone injection region in fluid communication with a permeate flowing region. An ozone transport conduit can fluidly connect a closed atmosphere of the settleable solids separator and the closed ozone treatment vessel.
The ultraviolet disinfection system can include one or more clear plastic tubes that are transparent to ultraviolet radiation and through which the reusable liquid fraction passes, ultraviolet lamps surrounding the plastic tubes, and an enclosure containing the assembly of tubes and lamps. The ultraviolet lamp apparatus can produce ozone in the air space surrounding the lamps. The ozone can be extracted from the enclosure, which can serve as an ozone generator. An ozone transport conduit can fluidly connect a closed atmosphere of the settleable solids separator and a closed ozone treatment vessel of the ozone treatment system. Exposure to ultraviolet radiation can directly kill organisms, and if dissolved ozone is contained in the liquid, it can create powerful oxidizing agents that further disinfect, remove odor and color, reduce biochemical oxygen demand of, and oxidize harmful chemical compounds in the liquid.
The apparatus can include a wastewater pump, such as a comminuting wastewater pump in fluid communication with the inlet of the settleable solids separator.
The apparatus can also include a flow restrictor in fluid communication with the concentrate outlet port of the membrane separation system. The flow restrictor can be used to regulate the flow of the process. Periodically, the flow restrictor can be used to retard flow so as to cause the liquid levels of both the vessel of the settleable solids separator and the equalization vessel to rise beyond the overflow ports of both vessels, thereby forcing accumulated scum layer and other floating material on the surface of the vessels to be discharged into the slurry fraction via a scum overflow and vent port that can be in fluid communication with a slurry fraction conduit. The slurry fraction conduit can be in fluid communication with the second outlet of the settleable solids separator. The outlet of the flow restrictor can be in fluid communication with either the settleable solids separator vessel or an equalization vessel.
In particular embodiments, the apparatus can include a solids treatment system. The solids treatment system can include an inlet port and an outlet port. The inlet port can be in fluid communication with the slurry fraction conduit. The solids treatment system can include a vessel with an inlet port in communication with the slurry stream, and an outlet port. The solids treatment system can have a volume sufficient to allow the settleable solids in the slurry stream an opportunity to settle and decompose by, for example, predominantly anoxic biological processes. The outlet port of the solids treatment system can be in fluid communication with the inlet of the settleable solids separator. The outlet port of the solids treatment system can be in fluid communication with the inlet of the gravity separator vessel.
In another aspect, the invention features an apparatus for treating wastewater containing settleable solids. The apparatus includes a vortex separator and an ozone treatment system. The vortex separator includes a closed separator vessel having an upper end, a lower end, and an outer wall connecting the upper end and the lower end, an inlet directed partially tangentially through the outer wall near the upper end of the vessel, a first outlet proximate to the upper end of the vessel, and a second outlet proximate to the lower end of the vessel. The ozone treatment system includes a closed ozone treatment vessel having a fluid inlet and an ozone injection region in fluid communication with a fluid flowing region. A fluid conduit fluidly connects the first outlet of the vortex separator to the fluid inlet of the ozone treatment system, and the closed separator vessel and the closed ozone treatment vessel are fluidly connected by an ozone transport conduit.
The method offers a simple, reliable, rapid, compact and inexpensive process for obtaining reusable water, which can overcome many of the deficiencies of conventional biological wastewater treatment processes. For example, the apparatus and method performs more reliably and efficiently than paper filter, membrane, or biological systems alone. The apparatus is a complete wastewater reclamation system that, among other things, can minimize conveyance costs, can avoid the use of inherently unreliable and maintenance-intensive wastewater treatments, can overcome certain limitations of past physical or chemical systems, can produce reusable or readily disposed residual byproducts, can be compact, economical, reliable, and odorless, and can produce high quality thoroughly disinfected water appropriate to various reuse applications, such as irrigation and other non-critical reuse applications, washing, cooling and other industrial uses, or aquaculture and for discharge to surface water bodies. The method an apparatus can also create an odorless environment in the surrounding of the apparatus. Accordingly, the wastewater reclamation system can be well suited for on-site or local applications in which the water produced is reused productively in the vicinity of the treatment plant.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.